Split out the node location search section of the node template.

This is so people can override it with a custom form if they want to say use miles instead of metres as requested in #50.
Add an optional custom template to node_location_search.tt

This allows people to add more location based searches to a node.
e.g. nearest tube station.
Merge pull request #55 from OpenGuides/50_breakout_node_distance_search

breakout node distance search